Acidly satirical British cartoonist Ralph Steadman is the subject of Charlie Paul’s engaging but uneven documentary, which also features—and is narrated by—Johnny Depp, whose devotion to the project derives from the fact that Steadman was an important collaborator with one of the actor’s heroes, gonzo journalist Hunter S. Thompson. “For No Good Reason” contains much engrossing material—most notably interviews with Steadman and footage of him happily showing how he goes about his work in his studio. But it’s burdened by material that seems extraneous, not least much of the footage of Depp, who took often is shown nodding amiably in response to Steadman and saying things like “Awesome” and “Amazing”—promptings that as an audience we don’t really need. Comments about Steadman by other famous folk like Terry Gilliam, Richard E. Grant and Tim Robbins also come across as unnecessary padding.

Depp’s presence is also indicative of the fact that Paul’s treatment sometimes seems determined to put the emphasis on Thompson than on Steadman. (Even the title is a quotation from Thompson.) True, once the two worked together for the first time in 1969 in a famous series on the Kentucky Derby, they became lifelong collaborators. And the picture uses the differences between them to make the shrewd observation that they meshed in an unusual way: Steadman, though quite conservative in his own lifestyle (unlike the grandiose, self-destructive Thompson) was actually more radical in his views, and more pointed and precise in expressing them in paint, than Thompson was in his writing.

And it’s with regard to that last point that “For No Good Reason” is most welcome. Steadman is a brilliant craftsman, as the numerous examples of his art (sometimes animated, unecessarily) demonstrate. But his painting was in the service of his beliefs, employing savage strokes to lambaste what he most detested—political skullduggery, inhuman violence, economic inequity—and its bold, seemingly anarchic spirit retains its freshness even after many years. (He also comes across as genuinely uncomfortable about how his work has become the stuff of merchandising.) And if Steadman sounds a bit rueful when he wistfully says that he wanted to use his brushes to change the world, he follows up the words with a self-deprecatory grin.

Unfortunately, Paul isn’t particularly subtle in getting that idea across, at one point having Steadman read from the Universal Declaration on Human Rights. He illustrated that document and obviously holds it dear, but it nonetheless feels like a ham-fisted directorial choice. So too does the selection of music, which doesn’t seem to have a great deal of relevance to Steadman and is often mixed too loud for comfort.

And this is, finally, an artistic biography. Though it traces Steadman’s resistance to authority to his youth, it doesn’t follow up that notion in any detail. Nor does it tell us anything at all about his personal life; his family receives nary a mention. Certainly some material in that area would have been appropriate; and a brief interview with his wife could easily have taken the place of a few of Depp’s admiring “Wow”s.

For all its flaws, however, “For No Good Reason” does showcase Steadman’s artistic influence and his personal convictions, and for that reason alone it’s worth welcoming.